The use of hyperosmolar media for the support of the growth of protoplasts, spheroplasts and L-forms of bacteria is well established (L. B. Guze, Microbial Protoplasts, Spheroplasts and L-forms, Williams and Wilkins, Baltimore, Md., 1968). The extensive application of hyperosmolar media to the detection of bacteremia is more recent: Am. J. Med. Tech., 35, 702-5 (1969); Microbiol., 19, 281-2 (1970); Am. J. Clin. Path., 57, 220-7 (1972); Abst. Ann. Meeting, Am. Soc. Microbiol., No. M48, 81 (1973).
Virtually all studies of clinical samples have utilized media in which sucrose is used to elevate the osmotic strength to 600 milliosmolar or higher. Alternative solutes to sucrose have had very limited study. Ionizable salts, e.g., sodium and potassium chloride, are of limited value and are not favored (Antonie van Leeuwenhoek, 36, 21-31 (1970). Glycerol penetrates microbial cell walls and is not useful (J. Gen. Microbiol., 82, 125-42 (1974).
Although the recovery rate of pathogenic bacteria from sucrose fortified media is satisfactory, sucrose has disadvantages in blood culture. At the 10% or higher concentrations used, sucrose media are more dense and more viscous than the base media. Settling of erythrocytes is therefore slower and less complete, and the visual detection of modest microbial growth can be difficult. After incubation for 24 hours or more, sucrose media also show hemolysis of the erythrocytes, and the resultant dark fluids are too opaque for the detection of modest microbial growth. Subculturing of these media is therefore too often necessary to ensure that growth is detected.
A medium which retains the growth promoting properties of high osmolarity sucrose media, free of these disadvantages, would provide the clinical microbiologist a tool that could allow more facile and more rapid detection of bacteremia.